Project Summary Eosinophilic gastrointestinal disorders (EGIDs) are a group of inflammatory diseases triggered by food or aero- allergens and characterized by an excessive accumulation and persistence of eosinophils within intestinal tissues and a Th2-dominant immune response. Despite a worldwide increase in prevalence, the natural disease course of EGIDs is unknown, and treatment options limited to food allergen avoidance and oral corticosteroids. EGID symptoms and treatments carry heavy social and psychological tolls, particularly in affected children. Eosinophils are innate immune leukocytes that constitutively home to lamina propria of the small and large intestine in the steady-state. Fundamental factors that govern excessive eosinophil accumulation and persistence within gastrointestinal tissues in EGID patients, and mechanisms whereby intestinal tissue-resident eosinophils might engage food or aero-allergens and participate in EGID pathogenesis remain speculative. At the core of this proposal are our two novel findings that: 1) Identify Notch signaling as a core pathway that orchestrates eosinophil migration and persistence within tissues; and 2) Demonstrate intestinal eosinophils capture intestinal lumen-derived antigen through a process requiring antigen-specific IgG and eosinophil-expressed Fc?RIII in vivo, constitutively express antigen presenting cell machinery, and co-localize with T cells following oral allergen challenge. A logical extension of our published and preliminary data, Aim I of this R01 proposal defines the mechanisms whereby Notch signaling regulates eosinophil migration and survival within tissues and tests the efficacies of targeting eosinophil-expressed Notch receptors in preventing EGIDs in vivo. Fully supported by our preliminary data, experiments in Aim II extend our findings that non-IgE humoral immunity provides a direct link between food allergen triggers and tissue eosinophils to test a new paradigm whereby intestinal eosinophils engage in antigen-driven degranulation and direct antigen presenting cell functions that impact the immunopathogenesis of EGIDs by affecting the local repertoire and spatial arrangement of CD4+ T cells. This proposal utilizes a number of genetic manipulations in Aims I and II to systematically test our hypotheses in vivo using three antigenically and anatomically distinct models of EGIDs. In a complementary parallel approach, Aim III utilizes eosinophils isolated from human ileal tissues and humanized transgenic mice to confirm the direct relevance of our data to human disease, and to evaluate the fidelity of the mouse as a model for antigen-driven functions of human intestinal eosinophils.